Solid state relay arrangement

ABSTRACT

A Triac connected in series circuit with an alternating current electrical load has its gate electrode connected to a secondary winding of a transformer the primary winding of which is connected to a source of alternating electrical current; when a related control switch is closed the primary winding causes an induced voltage in the secondary winding which is out of electrical phase with the source; the induced voltage is then sufficient to develop a triggering current, at least equal to the gate threshold current, which is applied to the gate electrode as the potential across the Triac swings through a zero potential.

United States Patent Platzer, Jr. 1 Oct. 24, 1972 [54] SOLID STATE RELAYARRANGEMENT [72] Inventor: George E. Platzer, Jr., 30720 Primary 9Rolmec w g Southfield, Mich. Assistant Examiner-David M. Carter [22]Filed: Dec. 22, 1969 [57] ABSTRACT PP 386,864 A Triac connected inseries circuit with an alternating current electrical load has its gateelectrode con- 52] us. Cl. ..307/2s2 B, 307/252 UA 307/305 a secmdarywinding "ansfmmer [51] Int Cl 6 17/00 primary winding of which isconnected to a source of [58] Fie'ld 252 UA alternating electricalcurrent; when a related control switch is closed the primary windingcauses an induced voltage in the secondary winding which is out [56]References cued of electrical phase with the source; the induced volt- IUNITED STATES PATENTS age is then sufficient to develop a triggeringcurrent, at least equal to the gate threshold current, which is3,320,518 5/1967 Weiss ..307/252 applied to the gate electrode as thepotential across 3,392,626 7/ 1968 Miller ..307/252 the Triac Swingsthrough a zero POtemiaL 3,418,489 12/1968 Platzer ..307/252 3,509,382 4/1970 Zgebyra ..307/305 8 Claims, 3 Drawing Figures PAIENIEnw 2 W2 3. 700923 IN VENTOR.

SOLID STATE RELAY ARRANGEMENT BACKGROUND OF THE INVENTION In the pastmechanical type electrical relays have been employed. Such relays wereusually constructed of a field coil, an armature responsive to theenergization of such a coil and a suitable set of mechanically actuatedelectrical contacts. As has been generally well known to those skilledin the art, such relays of the prior art have many disadvantages. Someof these, for example, are the accumulation of dirt on the moving parts,pitting of the electrical contacts, electrical arcing and, often, someslowness in the response time of overall relay assembly.

Solid state relay systems have been proposed by the prior art; however,such have not been widely accepted because they are often too costly forgeneral applica-' tion and often include and require rectifying bridgeswhich only further add to the cost of such prior art relay devices.

Accordingly, the invention as herein disclosed and described isprimarily concerned with the solution of the above as well as otherrelated problems.

SUMMARY OF THE INVENTION According to the invention, a solid state relayarrangement for an electrical circuit employing a source of alternatingelectrical potential for developing an alternating current, comprises agated solid state switching means for controlling the opening andclosing of circuit means containing a related alternating currentelectrical load, transformer means including at least one primarywinding and at least one secondary winding, said primary winding beingadapted for connection to said source, said secondary winding beingelectrically connected to one terminal and the gate electrode of saidsolid state switching means, and additional control switch means for attimes applying an. al ternating current flow from said source ofelectrical current to said primary winding in order to in accordancetherewith develop a flux field and induce a voltage and current flow insaid secondary winding, said induced voltage in said secondary windingbeing effective to apply a triggering current to said gate electrode ofsufficient magnitude to place said solid state switching means in aconductive state thereby closing said circuit means.

Various general and specific objects and advantages of'the inventionwill become apparent when reference is made to the following detaileddescription considered in conjunction with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS In the drawings, wherein for purposes ofclarity certain details and elements may be omitted from are views:

FIG. 1 is a schematic wiring diagram embodying a first embodiment of theinvention;

FIG. 2 is a schematic wiring diagram of a second embodiment of theinvention;and

FIG. 3 is a graph-illustrating, among other things, the phaserelationship'of the currents and voltages involved in the circuitry ofeither FIG. 1 or FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now in greater detailto the drawings, FIG. 1 illustrates an overall electrical circuit 10comprised basically of three sub-circuits 12, 14 and 16 which may beoperationally connected to each other, if desired, as by suitableconnectors schematically illustrated at 18, 20, 22 and 24.

Circuit 12 is comprised of a suitable source 26 of alternatingelectrical potential, for developing an alternating current, having itsoutput terminals 28 and 30 respectively connected to conductors 32 and34 leading to anormally open switch member 36, of a switch assembly 38,and connector 20. The fixed contact 40 of switch assembly 38 isconnected to connector 20 as by a conductor 42.

Circuit 16 may be comprised of a suitable source 44 of alternatingcurrent having its output terminals 46 and 48 respectively connected toconductors 50 and 52 which, in turn, lead to connector 24 and oneterminal 54 of an associated electrical load 56. The other terminal 58of load 56 is connected to connector 22 via electrical conductor 60. Forpurposes of disclosure, sources 26 and 44 are illustrated as beingseparate; however, especially as the description thereof progresses, itshould be apparent that such sources 26 and 44 may in fact be the samesingle source of alternating current.

Circuit 14 is comprised of a transformer 62 having a primary winding 64and a secondary winding 66 with terminals 68 and 70 of primary winding64 being respectively connected-to terminal 72 of a resistor 74 andconnector 20 via conductors 76 and 78. The other terminal 80 of resistor74 is connected to connector 18 by means of a conductor 82.

Terminals 84 and 86 of secondary winding 66 are respectively connectedto one end of a resistor 88 and to a conductor 90 leading to connector24. The other end or terminal 92 of resistor 88 is electricallyconnected, via conductor 94, to the gate electrode 96 of a Triac 98. Theother terminals l00iand 102 of Triac 98 are respectively connected toconductors 104 and 106 which lead to connector 22 and conductor 90.Generally, a Triac can be described as consisting of an N-P-N-P switchin parallel with a P-N-P-N switch formed in a single silicon crystal.The actionof a Triac is somewhat similar to two parallel and oppositelypoled silicon controlled rectifiers. Generally, in order to achieveconduction through the Triac 98,.there must be a voltageapplied acrossterminals and 1-02 anda control current at the control electrode or gate96.

Ideally, most of the voltage drop in the circuit 12 is across theprimary resistor 74 rather than across the primary winding 64 oftransformer 62 in order to thereby assure that the current in theprimary winding 64 will be in phase with the voltage of AC. source 26.Therefore, by application of Lenzs Law, it becomes apparent that voltageinduced in the secondary winding 66 will be 90-out of phase with the AC.voltage of source 26. Of course, sources 26 and 44 are in phase witheach other especially when, as previously mentioned, separatelyindicated sources 26 and 44 may be replaced by a single A.C. source.

Resistor 88, in the gate circuit of the Triac 98, is employed toestablish a limit to the gate current. For purposes ofexample, let it beassumed that Triac 98 has a required gate trigger current of 25.0milliamperes and that the transformer 62 has a l 1 turn ratio with a10.0 volt peak output. If now the AC. source or supply is rated at 120.0volts (R.M.S.) the peak voltage value will be:

(120.0 volts) l .414) 170.0 volts If the system is now designed for apeak current of 50.0 milliamperes, the gate current of Triac 98 will beabove the 25 .0 milliampere threshold value for about 45 on either sideof zero value for the supply voltage from the AC. source.

With the above, the value of the primary resistor 74 can be determinedas follows:

(170 volts/50 X 103 amps. =3,400.0 ohms,

while the value of the resistor 88 in the gate circuit can be determinedin the following manner:

10.0 volt/50 X 10 amp. 200.0 ohms OPERATION OF THE INVENTION Inconsidering the operation of the invention, reference will be made toboth FIGS. 1 and 3. Accordingly, when switch member 36 is closed, thecurrent through primary winding 64 may be considered to have acharacteristic sine curve substantially in phase with the supply voltageas illustrated by curve 110 of FIG. 3. (Since the sources 26 and 44, ifseparate sources are employed, will have substantially in phase outputvoltages, curve 110 can be considered as depicting either or both ofsuch output voltages of such sources 26 and 44.) Such voltage applied toterminals 18 and 20, as is well known, will develop a secondary voltage,generally depicted by curve 112 in FIG. 3, in the transformer secondarywinding 66. Further, since the secondary winding voltage and currentwill be in phase with each other, curve 112 can be considered asrepresenting either the secondary current flow or the secondary voltage.

' If a vertical line 114 is drawn through the intersection of the AC.supply or source voltage curve 110 with the horizontal axis or O"-line,such line when extended upwardly will intersect the maximum point (orvery nearly thereto) of the transformer secondary winding voltage curve112 as at 116. Similarly, if a second vertical line 118 is drawn throughthe intersection of the secondary winding voltage curve 112 with thehorizontal axis or O"-line, such line when extended downwardly willintersect the maximum point (or very nearly thereto) of the supplyvoltage curve 110 as at 120. The distance, D, between such lines 114 and118 is the phase shift between curves 110 and 112 which, in this case,is illustrated asbeing a phase shift.

If curve 112 is thought of as being the secondary winding voltage curve,then each of the relatively shortdash horizontal lines 112 and 124respectively intersecting curve 112, as at 126, 128 and 130, 132,depicts that particular magnitude or value of voltage (sometimesreferred to as threshold voltage) which will, through resistor 88,develop the required threshold current (which, for purposes ofillustration has been previously assumed to be 25 .0 milliamperes). .Ofcourse, if curve 1 12 is thought of as being the current in the Triacgate circuit, then such dash-lines 1 12 and 124 would represent theminimum or threshold current.

As can be seen, the invention provides, in effect, a current signal, tothe gate 96 of Triac 98, equal to or greater than the threshold currentvalue for a span of time measured horizontally as from point 126 topoint 128, during the first half cycle and horizontally as from point130 to point 132 during the second half of the cycle. If for ease ofreference, these are referred to as threshold or triggering currentpulses, then it can be seen that a very wide band triggering pulse isautomatically developed by the AC. source during each half of the cycleand that the width of such triggering pulses accommodates an extremelywide phase shift as might exist between curves 108 and 110 as mightoccur depending upon the degree of reactance within the load 56.

In view of the preceding, it can be seen that as the current from theAC. source through terminals and 102 of Triac 98 (represented by curvepasses through the 0 value of FIG. 3, the secondary winding developedvoltage and resulting current has already increased to a maximum valueas at point 1 16 of curve 112. Accordingly, the conditions for causingthe Triac 98 to become conductive are fulfilled. That is, a sufficienttriggering current, equal to or in excess of the gate threshold current,has been applied to the Triac gate 96 at the time that a zero potentialexists across the Triac terminals 100 and 102, and has remained applieduntil the potential across the Triac has increased to the point wherethe Triac can switch on. r g

The characteristic of a Triac is such as to remain conductive even aftertermination of the triggering current to the Triac gate; such conductionwill also terminate when the Triac terminals 100 and 102 once againreach a zero potential. However, as can be seen in FIG. 3, the pulse ortriggering current is again automatically established at point beforethe voltage (represented by curve 110) across Triac terminals 100 and102 again becomes zero potential as represented by intersection point134.

Therefore, it can be seen that once switch 36 is closed, Triac 98becomes conductive and remains conductive until such time as switch 36is again opened. Whenever, Triac 98 becomes conductive, the electricalload 56, of course, becomes energized. Accordingly, it should beapparent that the invention of FIG. 1 in effect discloses a solid statetype of electrical relay which would be classified as being normallyclosed.

FIG. 2 illustrates a second embodiment of the invention which might beclassified as being a normally open solid state relay. All elements inFIG. 2 WHICH are like or similar to those of FIG. 1 are identified withlike reference numbers.

From a comparison of FIGS. 1 and 2, it can be seen that the basicdifference therebetween resides in the provision of a circuit 13, inFIG. 2, comprised of a source 136 of A.C. current having its outputterminals 138 and 140 respectively connected via conductors 142 and 144to terminals 146 and 148 of a resistor 150 and a second primary winding152. The resistor 150 and primary winding 152 may then be connected toeach other as at a common terminal 154.

The operation of the embodiment of FIG. 2 is as explained with referenceto FIG. 1. However, the transformer 62a now has a second primary winding152,

connected so as to produce a flux opposing that produced by 64.Accordingly, whenever switch 36 is open, the closed circuit 13 iseffective to induce current flow into the secondary winding 66 in themanner described with reference to primary winding 64 of FIG. 1 therebycausing the Triac 98 to be in a continuously conductive state resultingin energization of load 56. However, because of the opposing fluxproduced by primary windings 152 and 64, whenever switch member 36 isclosed, the current flow through primary winding 64 effectively cancelsthe effect of the current flow through primary winding 152 whichresults, of course, in no induced voltage in secondary winding 66causing an absence of a triggering current at gate 96 thereby renderingTriac 98 non-conductive and deenergizing load 56. As in the case of theembodiment of FIG. 1, the sources of A.C. current 26, 44 and 136 may infact comprise a single source of A.C. current which,

-in view of the preceding description, should be apparent to thoseskilled in the art.

Both FIGS. 1 and 2 illustrate, in phantom line, a capacitor 160 situatedso as to have one side thereof connected to conductor 94 and its otherside connected to conductor 90. Such a capacitor, as well as otherdevices which should be apparent to those skilled in the art is employedto prevent the occurrence of spurious turn-on signals to the Triac gate96 arising out of possible voltage transients in the associatedcircuitry.

In FIG. 2, circuit 13 has been illustrated as being a totally closedcircuit, however, it should be apparent that a switch such as 36 couldbe placed within the circuitry of circuit 13. By adding such a switch, asingle device as shown by FIG. 2 could then be employed in any situationregardless of whether a normally open or a normally closed relay wasdesired. If a normally closed relay was desired, such switch placedwithin circuit 13 would be closed and permitted to remain closed whileswitch 36 of circuit 12 would be employed for causing the relay tobecome opened at selected periods of operation. If, however, a normallyopen relay was desired, such a switch placed in circuit 13 would bepermitted to remain open and the closing of the relay would beaccomplished by the closing of switch 36 within circuit 12.

Although only a select number of embodiments of the invention have beendisclosed and described it is apparent that other embodiments andmodifications of the invention are possible within the scope of theappended claims.

Iclaim:

1. A solid state relay arrangement for an electrical circuit employing asource of alternating electrical potential effective for producing analternating electrical current, comprising gated solid state switchingmeans for controlling the opening and closing of circuit meanscontaining a related alternating current electrical load, transformermeans including primary winding means and secondary winding means, saidsecondary winding means being electrically connected to one terminal andthe gate electrode of said solid state switching means, said secondarywinding means being adapted to have induced therein an induced voltage,said induced voltage being effective to develop and apply a triggeringcurrent to said gate electrode of sufficient magnitude to place saidsolid state switching means in a conductive state thereby closing saidcircuit means through said load, and said primary winding means beingadapted to be energized by said source for creating a flux field forinducing said induced voltage in said secondary winding means.

2. A solid state relay arrangement according to claim 1 wherein saidgated solid state switching means comprises a Triac having said oneterminal and a second terminal serially in said circuit means containingsaid related electrical load.

3. A solid state relay arrangement according to claim 1, wherein saidprimary winding means comprises at least one primary winding of saidtransformer means, and wherein said secondary winding means comprises atleast one secondary winding of said transformer means.

4. A solid state relay arrangement according to claim 1, wherein saidprimary winding means comprises at least first and second primarywindings, said first and second primary windings being effective torespectively produce upon energization by said source first and secondflux fields in opposition to each other so as to resultin no productionof an induced voltage in said secondary winding means whenever saidfirst and second flux fields are in coexistance.

5. A solid state relay arrangement according to claim 1, includingcontrol switch means effective to selectively open and close anelectrical circuit between said primary winding means and said source.

6. A solid state relay arrangement according to claim 4, includingcontrol switch means in circuit with at least one of said first andsecond primary windings, said control switch means being effective to attimes open said circuit and said one of said primary windings in orderto eliminate one of said flux fields and permit the other of said fluxfields to induce said induced voltage in said secondary winding.

7. A solid state relay arrangement according to claim 4, wherein saidfirst primary winding is adapted to be placed in closed circuit withsaid source, and wherein said second primary winding is adapted to beselectively placed in closed circuit with said source, and controlswitch means electrically connected between said source and said secondprimary winding for effecting said selective placement of said secondprimary winding in said closed circuit with said source.

8. A solid state relay arrangement according to claim 1, includingcapacitor means electrically connected to and in parallel with saidsecondary winding means.

1. A solid state relay arrangement for an electrical circuit employing asource of alternating electrical potential effective for producing analternating electrical current, comprising gated solid state switchingmeans for controlling the opening and closing of circuit meanscontaining a related alternating current electrical load, transformermeans including primary winding means and secondary winding means, saidsecondary winding means being electrically connected to one terminal andthe gate electrode of said solid state switching means, said secondarywinding means being adapted to have induced therein an induced voltage,said induced voltage being effective to develop and apply a triggeringcurrent to said gate electrode of sufficient magnitude to place saidsolid state switching means in a conductive state thereby closing saidcircuit means through said load, and said primary winding means beingadapted to be energized by said source for creating a flux field forinducing said induced voltage in said secondary winding means.
 2. Asolid state relay arrangement according to claim 1 wherein said gatedsolid state switching means comprises a Triac having said one terminaland a second terminal serially in said circuit means containing saidrelated electrical load.
 3. A solid state relay arrangement according toclaim 1, wherein said primary winding means comprises at least oneprimary winding of said transformer means, and wherein said secondarywinding means comprises at least one secondary winding of saidtransformer means.
 4. A solid state relay arrangement according to claim1, wherein said primary winding means comprises at least first andsecond primary windings, said first and second primary windings beingeffective to respectively produce upon energization by said source firstand second flux fields in opposition to each other so as to result in noproduction of an induced voltage in said secondary winding meanswhenever said first and second flux fields are in coexistance.
 5. Asolid state relay arrangement according to claim 1, including controlswitch means effective to selectively open and close an electricalcircuit between said primary winding means and said source.
 6. A solidstate relay arrangement according to claim 4, including control switchmeans in circuit with at least one of said first and second primarywindings, said control switch means being effective to at times opensaid circuit and said one of said primary windings in order to eliminateone of said flux fields and permit the other of said flux fields toinduce said induced voltage in said secondary winding.
 7. A solid staterelay arrangement according to claim 4, wherein said first primarywinding is adapted to be placed in closed circuit with said source, andwherein said second primary winding is adapted to be selectively placedin closed circuit with said source, and control switch meanselectrically connected between said source and said second primarywinding for effecting said selective placement of said second primarywinding in said closed circuit with said source.
 8. A solid state relayarrangement according to claim 1, including capacitor means electricallyconnected to and in parallel with said secondary winding means.